This invention relates to a clamping circuit or a clamper suitable for image processing.
For setting an analog output level to a desired external set voltage as in the case of a reference black level for a charge coupled device (CCD) output, a clamping circuit is used.
In a typical prior art clamping circuit, two differential amplifiers are connected in a loop, and a holding capacitor is provided at the junction between the differential amplifiers.
Since a differential amplifier used in such a circuit is required to have a high gain, the circuit construction becomes complicated and the occupation area on a semiconductor device is also large, thereby preventing miniaturization of the device. In addition, overshoot is produced during the clamping operation because the differential amplifier has a high gain, so that the entire system is likely to become unstable. Depending upon circumstances, defective phenomena such as oscillation, etc. may occur.